This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-098026, filed Mar. 31, 2000, the entire contents of which are incorporated herein by reference.
The present invention concerns a field emission type cold cathode device, a manufacturing method thereof and a vacuum micro device using the field emission type cold cathode device.
As field emission type cold cathode device, one using fullerene or carbon nanotube for emitter has been proposed (for instance, Jpn. Pat. Appln. KOKAI Publication No. 10-149760). Fullerene and carbon nanotubes allow to lower the driving voltage and improve the field emission efficiency as their tip curvature radius is small. In addition, they can operate at a low vacuum degree, as they are influenced little by the atmosphere dependency or residual gas.
Concerning methods for forming the aforementioned field emission type cold cathode device, a method for dispersing fullerene or carbon nanotube in an organic solvent, applying and contact bonding on a substrate, a method for directly depositing fullerene or carbon nanotube on a substrate, a method for dispersing fullerene or carbon nanotube in a thick film paste, printing and annealing under a high temperature (about 500 to 800xc2x0 C.), or the like are proposed.
However, when fullerene or carbon nanotube is contact bonded or deposited on a substrate, the adherence of fullerene or carbon nanotube is weak, and it is peeled off easily by a strong electric field applied to the emitter. Besides, when fullerene or carbon nanotube is formed by printing, the performance lowers or deteriorates due to high temperature annealing.
In addition, in contact boding, the patterning for cathode line formation is extremely difficult, because carbon is highly chemical-resistant, and etching is difficult. Otherwise, in a deposition method by CVD method or the like, catalyst of transition metal is required, and signal delay or the like is produced easily, because fullerene or carbon nanotube is required to be atomized, resulting in high resistance value. In the printing method also, signal delay or the like is produced easily, because of high film resistance, and in addition, difficulty of forming a thick film and, consequently, low resistance wiring.
Thus, field emission type cold cathode devices using fullerene or carbon nanotube as emitter have been proposed, conventionally, they were not necessarily sufficient in respect of reliability or performance.
An aspect of the present invention intends to solve the aforementioned problems, and has an object to improve the reliability or performance of a field emission type cold cathode device using fullerene or carbon nanotube for emitter.
A field emission type cold cathode device according to a first aspect of the present invention, comprises a substrate; and a metal plating layer formed on the substrate; wherein the metal plating layer contains at least one carbon structure selected from a group of fullerenes and carbon nanotubes, the carbon structure is stuck out from the metal plating layer and a part of the carbon structure is buried in the metal plating layer.
The field emission type cold cathode device further may comprise a conductive layer formed between the substrate and the metal plating layer.
In the field emission type cold cathode device, the metal plating layer may be selected from a group of nickel, chromium and copper.
In the field emission type cold cathode device, the metal plating layer may be formed by either electroplating processing or electroless plating processing.
According to an aspect of the present invention, the metal layer is firmly fixed to the support substrate, and further fullerene or carbon nanotube is firmly fixed to the metal plating layer as a part of fullerene or carbon nanotube is buried in the metal plating layer. In other words, among fullerene or carbon nanotube contained in the metal plating layer, fullerene or carbon nanotube having protrusions (functioning substantially as electron emission section) on the surface of the metal plating layer is firmly fixed to the metal plating layer, because the portion under the protrusion is buried in the metal plating layer. Consequently, an adhesion resistance that can resist sufficiently against a strong electric field applied to the emitter can be obtained, and it becomes possible to obtain a high performance field emission type cold cathode device excellent in field emission stability.
Here, the metal plating layer (metal plating film) obtained by plating processing is fine, and better in conductivity and hardness, compared to the metal film obtained by sputtering method or printing method. As for the conductivity, the metal plating film is almost equivalent to bulk metal (equal or superior to about 99% of bulk metal conductivity), and lower in resistance compared to sputtered metal film (about 30 to 90%), and thick film printed metal film (about 10 to 20%). Concerning the hardness, when compared in Vickers hardness and Brinell hardness, the metal plating film is almost equivalent to the bulk metal (equal or superior to about 90%) and can be about 10 times in some cases, and extremely harder than the sputtered metal film and thick film printed metal film.
Further, the metal plating film can be formed in an almost even thickness, even if the surface to be plated is rough. For example, the metal plating film formed on the cathode line surface can make the film thickness almost equivalent at the top and the side of the cathode line.
Also, as the plating processing is performed at a low temperature, the metal plating film allows to obtain an emitter with less performance loss or deterioration. In addition, as it allows to obtain a high conductive film and to increase the thickness, the resistance of the cathode line can be lowered, and signal delay or the like can be suppressed. Moreover, as patterning is easy, the cathode line can be created easily.
Besides, when a convex emitter structure is formed using metal plating film, the electron emission point can be fixed easily, as electric field is concentrated to the convex tip section. In addition, as convex metal plating layer can be separated easily from the mold by lubricating effect of fullerene or the like, mold wear or damage can be suppressed even when the mold is used repeatedly.
Moreover, in the field emission type cold cathode device, the carbon nanotubes may have a conductive material inside. The conductive material is preferably a constituent of a plating liquid used for forming the metal plating layer. The conductive material is preferably selected from Mo, Ta, W, Ni, Cr, Fe, Co, Cu, Si, LaB6, AlN, GaN, carbon, graphite and diamond.
Thus, the formation of the conductive material section inside a hollow structure that the carbon nanotube has, makes the conductive material work as core material, allowing to increase the carbon nanotube mechanical resistance. Especially, the formation of conductive material section with a content of plating liquid used to form the metal plating layer, allows to perform plating and forming the conductive material section in parallel, and consequently, to simplify the process.
Here, in the field emission type cold cathode device, the metal plating layer may contain additive material for increasing resistance of the metal plating layer. The additive material is preferably selected from boron, phosphorus and polytetrafluoroethylene (PTFE). The additive material, blended (dispersed preferably) simple or in the form of compound in the plating liquid, can be contained easily in the metal plating layer, when the metal plating layer is formed by plating.
When the emitter tip is different in curvature radius, shape or the like, the field emission characteristics become uneven because of different electric field strength distribution. As mentioned above, when the resistance of the metal plating layer is increased by including additive material in the metal plating layer, the voltage drops due to the metal plating layer. As the result, even when the emitter tip is different in curvature radius, shape or the like, the electric field strength distribution of the emitter tip is evened by so-called resistive ballasting effect, allowing to improve considerably the field emission stability and evenness.
A vacuum micro device according to a second aspect of the present invention, comprises: a substrate; a metal plating layer formed on the substrate, the metal plating layer containing at least one carbon structure selected from a group of fullerenes and carbon nanotubes, and the carbon structure being stuck out from the metal plating layer and a part of the carbon structure being buried in the metal plating layer; and an electrode disposed separately from the substrate, the electrode being applied a higher electrical potential than an electrical potential applied to the metal plating layer.
The vacuum micro device preferably further comprises a conductive layer formed between the substrate and the metal plating layer.
A vacuum micro device according to a third aspect of the present invention, comprises a first substrate; a conductive layer formed on the first substrate; a metal plating layer formed on the conductive layer, the metal plating layer containing at least one carbon structure selected from a group of fullerenes and carbon nanotubes, and the carbon structure being stuck out from the metal plating layer and a part of the carbon structure being buried in the metal plating layer; a second substrate opposed to the first substrate; an electrode formed on the second substrate, the electrode being applied a higher electrical potential than an electrical potential applied to the metal plating layer; and a luminescent material formed on the electrode.
The vacuum micro device preferably further comprises an insulation layer formed on the substrate; and a gate electrode formed on the insulation layer and between the metal plating layer and the electrode.
A manufacturing method of field emission type cold cathode device according to a fourth aspect of the present invention, comprises immersing a substrate in a plating liquid containing at least one carbon structure selected from a group of fullerenes and carbon nanotubes; and forming a metal plating layer on the conductive layer, wherein the carbon structure is stuck out from the metal plating layer and a part of the carbon structure is buried in the metal plating layer.
The manufacturing method preferably further comprises forming a conductive layer on a substrate before immersing the substrate.
A manufacturing method of field emission type cold cathode device according to a fifth aspect of the present invention, comprises forming a conductive layer on a first substrate having concaves; immersing the first substrate in a plating liquid containing at least one carbon structure selected from a group of fullerenes and carbon nanotubes; forming a metal plating layer on the conductive layer, the carbon structure being stuck out from the metal plating layer and a part of the carbon structure being buried in the metal plating layer; pressing a second substrate to the first substrate sandwiching the metal plating layer; and removing the first substrate from the second substrate leaving the metal plating layer on the second substrate.
In the manufacturing methods of the field emission type cold cathode device, the plating processing is preferably one of electroplating processing and electroless plating processing. Especially, when the metal plating layer is formed by electroplating, the carbon nanotube can easily be oriented vertically along the line of electric force. Consequently, the proportion of carbon nanotube oriented vertically can be increased, and the field emission efficiency and the evenness of field emission can be enhanced.